Various ratchet drives are known in the art in which a ratchet gear mounted on a support is turnable about it axis, and a lever pivotable about a second axis, extending laterally from and parallel to the axis of the ratchet gear is mounted on the support for movement between a forward stroke and a return stroke. The lever carries at least one drive pawl which is mounted on one of the ends thereof on the lever tiltable about an axis spaced from the second axis and this pawl engages with the other end thereof the ratchet gear. When the lever is now tilted, by hand or by any mechanical means connected thereto, along its forward stoke, the free end of the pawl will engage a tooth of the ratchet gear to drive the latter in one direction, whereas during the return stroke, the pawl will ratchet over the adjacent tooth, so that the ratchet gear will be turned through a predetermined angle only during the forward stroke of the lever. In this known construction a holding pawl is usually provided which engages a tooth of the ratchet gear during the return stroke of the lever, to prevent turning of the ratchet gear in opposite direction during the return stroke of the lever and during ratcheting of the drive pawl over a tooth of the ratchet gear.
Such known ratchet drives may be used for many purposes and especially in a wrench for turning a threaded connector. In this case the ratchet gear may be provided with a polygonal passage therethrough, coaxial with the second pivot axis, for engagement with a polygonal head of a threaded connector to be turned, or with a polygonal drive connection projecting beyond the support, on which a standard socket for engagement with the polygonal head of the threaded connector is exchangeably mounted to be turned during turning of the ratchet gear. In such a construction fluid operated cylinder and piston means are interconnected between the support and the lever for tilting the lever between the forward and the return stroke during reciprocation of the piston in the cylinder of the unit.
The evident disadvantage of this known ratchet drive is that the ratchet gear will be turned only during the forward stroke of the lever, while remaining stationary during the return stroke of the latter.